The invention pertains to an article that has a wear-resistant coating as well as to a process for producing such article that has a wear-resistant coating. More specifically, the invention pertains to an article that comprises a substrate and a wear-resistant coating as well as to a process for producing such article that comprises a substrate and a wear-resistant coating.
In industrial processes, components of machinery and the like are often times subjected to wear. The same is true for many other articles in that they are often times subjected to wear. It has proven to be beneficial to protect these articles (including components) from wear. A well-accepted way to provide such protection against wear of an article is to apply a wear-resistant coating thereto.
One common method of applying a wear-resistant coating is by a thermal spray method. Thermal spray methods include processes that use detonation guns, high velocity oxygen flame spraying, plasma spraying, wire arc spraying, and flame spraying. There are, however, disadvantages associated with applying coatings via thermal spray methods. Except for vacuum plasma spraying, thermal spraying exposes the powders being sprayed to oxygen or water vapor so as to result in the formation of metal oxides that can be detrimental to the coating. There is a limitation to the scope of the articles that are suitable for coating via thermal spray methods because there must a line of sight between the end of the spray nozzle and the surface to be coated. Further, if the angle of impingement of the spray on the substrate is not constant, it is possible to deposit undesirable non-uniform coatings. U.S. Pat. No. 4,173,685 to Weatherly discloses the application of a wear and corrosion resistant coating to a substrate via a plasma or a d-gun technique.
Another process for applying wear-resistant coatings is described in U.S. Pat. No. 3,743,556 to Breton et al. The '556 Breton et al. patent discloses a process for applying a wear-resistant coating that first applies a cloth that contains particles of tungsten carbide to a surface that requires protection against wear. Second, another piece of cloth that contains particles of a braze alloy is positioned over the cloth that contains the carbide particles. The substrate with the two layers of cloth is placed in an inert-atmosphere furnace and then heated to the brazing temperature of the braze alloy. The braze alloy infiltrates down into the carbide particles and brazes them to each other and to the substrate. Although this process produces a wear-resistant coating, this process has limitations with respect to applying a thin coating layer, as well as limitations as to the geometry of the component since the component must be accessed with fingers or tools. The cloth process also can sometimes present seams in the wear-resistant coating that can result in structural discontinuities in the carbide coating.
U.S. Pat. No. 6,649,682 B1 to Breton et al. discloses a paint system and process for hardfacing metal surfaces. In the '682 Brenton et al. patent, a paint that includes a dispersion of hard particles is first applied as a coating to the surface of the substrate. Next, a paint including a dispersion of braze alloy is applied over the layer of hard particles. The substrate is then heated to cause the braze alloy to melt and infiltrate into the hard particles thereby bonding them to the metallic surface. The '682 Brenton et al. patent also discloses an embodiment of the process wherein a first layer of adhesive is applied to the substrate and a hardfacing powder is then applied to the adhesive. A second layer of adhesive is applied and a braze alloy powder is applied to the second adhesive. The substrate is then heated whereby the braze alloy melts and infiltrates into the hard particles so as to bond them to the metallic surface. In a third embodiment of the '652 Brenton et al. patent, a hardfacing alloy powder containing precipitated intermetallic hard compounds is made into a paint and applied to the surface that is to be protected. After drying, the paint is heated to from a coating. In a fourth embodiment, hardfacing particles and braze alloy powder are made into a paint and applied to the surface to be protected. The paint is then dried and heated to form the coating.
In a process such as that disclosed in '682 Breton et al. patent, in order to obtain a layer of the paint that includes a dispersion of hard materials that has sufficient thickness, it takes multiple coats (or dips) of the substrate into the paint to achieve the necessary cladding thickness. At sharp corners or edges of the substrate the paint has a tendency to pull away which results in a thinner cladding and a premature wear in these areas adjacent to the sharp corners or edges of the substrate.
It would thus be desirable to provide a coating process, as well as an article produced by the process, wherein the coating is not subject to oxidation such as is the case for coatings applied by thermal spray techniques.
It would thus be desirable to provide a coating process, as well as an article produced by the process, wherein the coating can be applied in a consistent fashion to the substrate so as to result in a uniform coating
It would thus be desirable to provide a coating process, as well as an article produced by the process, wherein the coating can be a relatively thin coating.
It would thus be desirable to provide a coating process, as well as an article produced by the process, wherein the coating can be applied to components or surfaces of components that are not accessible (or easily accessible) by hand or tools.
It would thus be desirable to provide a coating process, as well as an article produced by the process, wherein the wear-resistant coating is without seams.
It would thus be desirable to provide a coating process, as well as an article produced by the process, wherein it would not be necessary to use multiple coats or dips of a coating paint on a substrate to achieve the necessary coating (cladding) thickness.
It would also be highly desirable to provide a coating process, as well as an article produced by such process, wherein the thickness of the coating (or cladding) is sufficient at sharp corners or edges of the substrate so as to provide adequate wear resistance in these areas.
It would also be highly desirable to provide a coating process, as well as an article produced by such process, wherein the thickness of the coating (or cladding) at selected locations can be varied so that the substrate can have a coating that has a selectively variable thickness.